Recent advances in computer performance have enabled graphic systems to provide more realistic graphical images using personal computers, home video game computers, handheld devices, and the like. In such graphic systems, a number of procedures are executed to “render” or draw graphic primitives to the screen of the system. A “graphic primitive” is a basic component of a graphic picture, such as a vertex, polygon, or the like. Rendered images are formed with combinations of these graphic primitives. Many procedures may be utilized to perform 3-D graphics rendering.
Specialized graphics processing units (e.g., GPUs, etc.) have been developed to optimize the computations required in executing the graphics rendering procedures. The GPUs are configured for high-speed operation and typically incorporate one or more rendering pipelines. Each pipeline includes a number of hardware-based functional units that are optimized for high-speed execution of graphics instructions/data, where the instructions/data are fed into the front end of the pipeline and the computed results emerge at the back end of the pipeline. The hardware-based functional units, cache memories, firmware, and the like, of the GPU are optimized to operate on the low-level graphics primitives (e.g., comprising “points”, “lines”, “triangles”, etc.) and produce real-time rendered 3-D images.
The real-time rendered 3-D images are generated using raster display technology. Raster display technology is widely used in computer graphics systems, and generally refers to the mechanism by which the grid of multiple pixels comprising an image are influenced by the graphics primitives. For each primitive, a typical rasterization system generally steps from pixel to pixel and determines whether or not to “render,” or write a given pixel into a frame buffer or pixel map, as per the contribution of the primitive. This, in turn, determines how to write the data to a display buffer representing each pixel.
Various traversal algorithms and various rasterization methods have been developed for computing from a graphics primitive based description to a pixel based description (e.g., rasterizing pixel-to-pixel per primitive) in a way such that all pixels within the primitives comprising a given 3-D scene are covered.
Typical solutions involve generating pixels in a unidirectional manner by systematically stepping across a scene (e.g., from left to right) line by line, and visiting each pixel of the scene. A degree of coverage for each pixel is determined as per the contribution of the various primitives comprising the scene. Other traditional solutions involve utilizing per pixel evaluation techniques to closely evaluate each of the pixels comprising a display and determine which pixels are covered by which primitives.
Once the primitives are rasterized into their constituent pixels, these pixels are then processed in pipeline stages subsequent to the rasterization stage where the rendering operations are performed. Generally, these rendering operations assign a color to each of the pixels of a display in accordance with the degree of coverage of the primitives comprising a scene. The per pixel color is also determined in accordance with texture map information that is assigned to the primitives, lighting information, and the like.
A problem exists however with the ability of prior art 3-D rendering architectures to scale to handle the increasingly complex 3-D scenes of today's applications. Computer screens now commonly have screen resolutions of 1920×1200 pixels or larger. The prior art rasterization solutions are increasingly becoming a bottleneck to the 3-D rendering process. As display screens inexorably increase in size, for example, to 1920 pixels wide and larger, the prior art line-by-line stepping and per pixel evaluation solutions for rasterization increasingly need larger resources to handle the computational loads. To handle such large screen sizes, the rasterization resources of a GPU needs to handle a large number of per primitive evaluation operations (e.g., polygon edge equations) on a per clock cycle basis, and the per primitive evaluation operations are required to address a correspondingly large number pixels. Thus, typical prior art GPUs do not have adequate rasterization resources to scale to large screen sizes while maintaining acceptable real-time 3-D rendering performance.
Traditional methods of increasing 3-D rendering performance, such as, for example, increasing clock speed, have negative side effects such as increasing power consumption and increasing the heat produced by the GPU integrated circuit die. Other methods for increasing performance, such as incorporating large numbers of parallel execution units for parallel execution of GPU operations have negative side effects such as increasing integrated circuit die size, decreasing yield of the GPU manufacturing process, increasing power requirements, and the like.
Thus, a need exists for a rasterization process that can scale as graphics application needs require and provide added performance without incurring penalties such as increased power consumption and/or reduced fabrication yield.